The Boogie Board

Discussion Forum for Mesa Boogie Products
It is currently Mon Oct 15, 2018 11:22 pm

All times are UTC - 6 hours [ DST ]




Post new topic Reply to topic  [ 7 posts ] 
Author Message
 Post subject: How to rebias an amp
PostPosted: Fri Jul 27, 2007 6:14 am 
Offline
Mark II

Joined: Wed Jun 27, 2007 2:49 pm
Posts: 63
Location: Bedfordshire, England
Apologies if this has already been covered but I wondered if anyone knew of a website that explains in really SIMPLE tems, how to go about rebiasing an amp?
I have a Koch Twintone II that runs on 2EL34s and the manufatcturers warn of death, disease and destruction to anyone either not using their valves (tubes) or trying to do it without the aid of a tech who would no doubt charge a large amount of money.
Thanks very much


Top
 Profile  
 
 Post subject:
PostPosted: Fri Jul 27, 2007 11:36 am 
Offline
Mark II
User avatar

Joined: Tue Mar 06, 2007 12:30 pm
Posts: 118
Location: Nashville, TN
I suggest you read Randall Aiken's stuff as a starting point here:

www.aikenamps.com

Go to the Tech section. This will get you started in understanding what bias is and the difference between fixed and cathode biasing.

Then go to:

www.duncanamps.com/technical/lvbias.html

What can scare off most non-techies is the math......

There are plenty of resources available for those interested.

The word of caution:

There are dangerous voltages within your amp. If you do not know what the components in your amp are, I'd suggest that you do not attempt anything...the voltages inside are lethal! :shock:

THEY WILL KILL YOU!


Top
 Profile  
 
 Post subject:
PostPosted: Sat Jul 28, 2007 7:02 am 
Offline
Mark II

Joined: Wed Jun 27, 2007 2:49 pm
Posts: 63
Location: Bedfordshire, England
Thanks very much for the links.
Way too technical for me. I like (need) articles with lots of brightly coloured pictures!!!!
The potential for death is obviously a factor that I would have to take into account (don't want my ex-wife getting her hands on my meagre savings just yet!)
I'll just have to find a local tech and hope I don't get ripped off


Top
 Profile  
 
 Post subject:
PostPosted: Sun Jul 29, 2007 7:04 pm 
Offline
Mark II
User avatar

Joined: Wed Jul 25, 2007 10:34 pm
Posts: 56
go to www.eurotubes.com and check out the menu, there's a few videos that explain pretty simply how to rebias.


Top
 Profile  
 
 Post subject:
PostPosted: Mon Jul 30, 2007 2:47 pm 
Offline
Mark II

Joined: Wed Jun 27, 2007 2:49 pm
Posts: 63
Location: Bedfordshire, England
Thanks very much.
Now I like video. Much easier to understand!


Top
 Profile  
 
 Post subject: Re:
PostPosted: Thu Dec 21, 2017 2:11 am 
Offline
Bottle Rocket

Joined: Thu Dec 21, 2017 2:03 am
Posts: 3
fitz8005 wrote:
go to http://www.eurotubes.com and check out the menu, there's a few videos that explain pretty simply how to rebias.


Thanks for your sharing! I appreciate this.

_________________
khung ảnh
bộ tranh treo tường đẹp
http://kutegiagoc.com


Top
 Profile  
 
 Post subject: Re: How to rebias an amp
PostPosted: Fri Feb 09, 2018 5:20 am 
Offline
Mark II

Joined: Fri Jul 28, 2006 5:58 pm
Posts: 104
Location: Europe
Bias in tube amps is necessary for safe operation of the output tubes. Generally this means that the grid must be at a lower voltage than the cathode.

In amps with grid bias (often referred to as "fixed bias"), the cathodes are at ground (= 0V) and a negative voltage is applied to the grids of the power tubes. "Biasing" means adjusting the negative voltage so that the idle current of the tube is in the safe zone of operation. Since different tubes draw different amounts of current the negative voltage may have to be adjusted upwards or downwards. Some amps have a trimpot inside to do that adjustment. Mesa Boogie amps usually do not have the pot to adjust, so you have to either use different tubes or change a resistor in the bias circuit to adjust. Keep in mind that this is not a user serviceable adjustment unless you know what you are doing.

Cheers Stephan


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 7 posts ] 

All times are UTC - 6 hours [ DST ]


Who is online

Users browsing this forum: No registered users and 3 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum

Search for:
Jump to:  
Powered by phpBB® Forum Software © phpBB Group